Why Haven’t All Humans Become Immune to Pollen by Now, After Many Years of Evolution?

Pollen is the reason for most seasonal allergies. But humans have been around plants for hundreds and thousands of years. So why haven’t we become immune to pollen by now?
Read the following in-depth answers to find out the science behind it.


Allergies are caused by your immune system reacting to specific molecules.Your immune system has several varieties of antibody (the parts that detect pathogens and cause immune reactions).
Five in fact:

  • IgA
  • IgD
  • IgE
  • IgG
  • IgM

IgE is the antibody which is associated with allergies (an overreaction by this antibody). Interestingly; IgE is only found in mammals – making it ‘young’ (on the evolutionary timeline) compared to those found in fish, reptiles, and insects.Part of the theory behind allergies considers that IgE is ‘new’, its cutting edge, and could be considered an work-in-progress (in evolutionary terms).


Why Haven't All Humans Become Immune to Pollen by Now, After Many Years of Evolution?

Allergies are a result of the over active immune system. ‘Developing immunity’ isn’t really the problem. Many plants we are allergic to are not plants that we co-evolved with. Actually they are exactly the ones we co-evolved with… much of the same grasses and trees have been aroumd for hundreds of thousands of years or more. Evolution does not have a plan. Evolution does not optimize. Evolution is not even a process. Evolution is the result of natural selection. When a trait makes an animal stronger than the rest it becomes more successful at passing on its genes and the trait remains. Most traits are not perfect, they just werent enough to prevent offspring.


The immune system relies on encountering pathogens during the early stages of life in order to properly develop. This means that it needs to encounter all kinds of things, harmful or not, in order to figure out which ones are worth fighting and which ones are harmless.

Why Haven't All Humans Become Immune to Pollen by Now, After Many Years of Evolution?

There is a theory that we have achieved such a level of cleanness in our homes that sometimes the immune system cannot develop properly, and becomes prone to false positives, such as pollen or many other things. People who grow up in a more dirty environment usually don’t tend to develop allergies as much as those who grew up in clean environments. If the theory is true, then it makes sense that this condition is fairly recent in human history, so evolution would not have had time to “figure it out” yet.


Before sanitation became common, IgE was used to fight off parasitic worms in humans. But as we became more sanitized IgE didn’t have much use anymore because of less worms obviously. So now IgE attacks allergens causing our immune system to give a disproportionate reaction aka allergies.
So it’s kind of a backwards evolution.


You’re living in unnatural conditions. Our immune system is evolved to be suitable for life in an environment full of dirt and animals, insect bites and the associated foreign fluids, and with our bodies containing numerous parasitic infections e.g. tapeworms, lice. People who live in similar conditions today don’t get allergies.

Why Haven't All Humans Become Immune to Pollen by Now, After Many Years of Evolution?

For some people – like you – when the immune system can’t detect any shit, dirt or parasites, then it “decides” that the problem must be that it’s not looking hard enough (because from the evolutionary perspective, there always was dirt, shit and parasites to be found), it tries harder and attacks the most suspicious thing it can detect, which often is pollen.


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